GPS systems are used to determine or fix the position of a receiver using signals transmitted simultaneously from several satellites. FIG. 1 illustrates part of a conventional GPS system 10 that can be used to fix the position of a receiver 12, using satellites S.sub.1 -S.sub.N. The receiver 12 is able to receive the transmissions of those satellites that are "in view" (i.e., not blocked by the curvature of the earth). The receiver 12 uses the arrival time differences between the received simultaneously transmitted signals, along with satellite Doppler and position data and other ephemeris data embedded in the simultaneously transmitted signals, to calculate the position of the receiver 12. As is well known, GPS systems typically assign unique pseudorandom sequences for each satellite in the system. The psuedorandom sequences are repeated in each GPS satellite transmission at a set rate, and are used in determining pseudoranges (i.e., relative time delays between received satellite transmissions and a local clock in the receiver 12). The pseudoranges are then used in calculating the location of the receiver 12.
As shown in FIG. 2, some of these conventional systems (referred to herein as reference GPS network systems) use a reference GPS base station 20 that takes a snapshot of the GPS data, which is then sent to a remote unit (RU) 22. Although only one reference GPS base station is shown in FIG. 2, a reference GPS network system typically includes a large number of base stations. The reference GPS network performs some initial processing of the GPS signals received from the satellites. In particular, each reference GPS base station receives the satellite GPS signals via a GPS antenna 24. Data from the processed GPS signals (i.e., the aiding data) is transmitted to the RU 22 through a wireless link, via an antenna 25. The RU 22 receives the processed GPS signals via the wireless link using an antenna 25. The RU 22 also receives the GPS signals from the satellites using a GPS antenna 28. The RU 22 can then relatively quickly and accurately calculate its position using the received GPS signals from the satellites and the corresponding processed GPS data from the base station 20. One such conventional system is disclosed in U.S. Pat. No. 5,663,734 issued to Krasner.
However, one problem with this conventional reference GPS network system is that when a location fix is requested by a RU, the network sends out the satellite data individually to the requesting RU. This system of sending satellite data in response to individual requests is a relatively inefficient use of the bandwidth of the wireless link. Consequently, there is a need for a wireless link that efficiently uses its available bandwidth.